1. Field of the Invention
The present invention relates to a polyolefin resin composition suitable for producing effectively an oriented polyolefin resin film which is excellent in transparency, slipperiness and antiblocking property, and an oriented polyolefin resin film using the same.
2. Prior Arts
Oriented polyolefin resin films, especially oriented polypropylene films, have found application in food packing, fiber packing and other wide purposes because of their excellent transparency and mechanical properties. These excellent oriented polypropylene films have, however, not been free from fault; when the films are overlapped, they adhere to with each other causing the so-called blocking phenomenon and therefore cause a problem in that the packing-work efficiency is significantly lowered.
Conventionally, methods have been proposed in which a fine powdery inorganic substance as an antiblocking agent (hereinafter referred to as "ABA") is added to a polypropylene, the mixture is kneaded and molded into a sheet followed by orientation in order to improve slipperiness and the antiblocking property of the oriented polypropylene resin film. Those methods include a method which adds zeolite, magnesium silicate or the like (for example, JP-B-53-16134 and JP-B-48-14423), and a method which adds fine powdery silica (for example, JP-B-63-58170 and JP-A-4-288353). Since, however, the fine powdery inorganic substances are easily agglomerated and the affinity between the polypropylene resin and the inorganic substance is insufficient, there is a problem in that voids are produced during orientation around the inorganic substance acting as a nucleus, resulting in inferior transparency represented by LSI (light scattering transmission intensity).
In order to improve the drawbacks of these films containing the fine powdery inorganic substance ABA, methods have been proposed in which oriented films are obtained after dispersing a fine powdery high molecular substance ABA in the polypropylene resin (for example, JP-A-57-64522, JP-A-5-214120, JP-A-6-107868, JP-A-7-178805, JP-A-7-196819 and the like). In these methods, however, LSI may become inferior because of voids produced during orientation and an insufficient affinity between the polypropylene resin and the high molecular substance ABA, or the transparency of the film represented by haze may become inferior because of a large difference in refraction index between the polypropylene resin and the high molecular substance ABA. Further, there is a problem in that antiblocking property of the oriented film is not sufficient because of an insufficient degree of crosslinking.
Under these circumstances, the present inventors have conducted extensive studies for improving slipperiness and the antiblocking property without accompanying significant damage regarding transparency. As the result, they have discovered that a polyolefin resin composition which meets the above requirement and an oriented film therefrom can be obtained by using as an ABA a crosslinked polymer bead having a specific structure and thus completed the present invention.